package 环形链表;
/**
 *
 * Definition for singly-linked list.
 * class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) {
 *         val = x;
 *         next = null;
 *     }
 * }
 */
class ListNode {
      int val;
      ListNode next;
      ListNode(int x) {
          val = x;
          next = null;
      }
  }
public class Solution {
    public boolean hasCycle(ListNode head) {
        if(head==null||head.next==null){
            return false;
        }
        ListNode fast = head.next;
        ListNode slow = head;
        while(fast!=slow){
            if (fast==null||fast.next==null){
                return false;
            }
            fast=fast.next.next;
            slow=slow.next;
        }

        return true;
    }
}

